For decades information has been stored on magnetic tape medium using tape drives. Initially the magnetic tapes were wound about large reels in similar manner as film for early film projectors. In more recent years the magnetic tape has typically been housed in a cartridge or cassette, extending internally in the cartridge from a supply reel to a take-up reel. In these cartridge applications, typically a leader tape attaches to the reel. A splicing tape then connects the leader to the magnetic tape, which in turn wraps around the reel. Cartridges may contain a supply reel only, or a supply reel and take up reel.
In some systems, the magnetic tape has longitudinal tracks recorded thereon (e.g., tracks that extend along the major length dimension of the tape). In other systems, the path of the magnetic tape is such that the tape is at least partially wrapped around a drum in a manner to transduce helical stripes or tracks on the magnetic tape.
For example, in some digital data storage formats a tape coated with a magnetic medium is moved by a motor-driven capstan in a read/write mechanism along a path extending between two spools or reels and wrapped partially around a transducer contained in the mechanism and comprising a rotating drum carrying one or more electromagnetic heads. The plane of rotation of the drum is disposed at an angle to the plane of movement of the tape, so that each head traverses the tape along successive tracks extending across the width of the tape at an angle to its centreline.
Data is written to the tape in tracks. Each track has a number of sections that are commonly refered to as fragments. A fragment carries a portion of the user data that is stored on the tape and has a fragment number for identification amongst the fragments of the same track. The fragment number of a fragment unequivocally identifies the fragment within the fragments of the track. While fragments of different tracks can have identical fragment numbers, each fragment number can only occur once in each track.
U.S. Pat. No. 6,229,659 shows a tape drive for storing data on magnetic tape along successive tracks extending obliquely across the tape, in each of several areas including a lead-in area, a data area and an end-of-data (EOD) area. Each track comprises successive blocks or fragments of data, and each fragment has a header containing a synchronization byte, six information bytes and two parity bytes. The information bytes include a fragment identifier, an area ID sub code identifying the area in which the fragment is located, and various other sub codes relating to logical structure of the data. The inclusion of an area ID sub code and logical structure sub codes in the (compact) header of every fragment facilitates reliable searching of the data stored on the tape at high tape advance speeds. U.S. Pat. No. 6,715,033 shows a similar helical scan tape drive apparatus.